1. Field of the Invention
The present invention relates to a needle roller bearing comprising an outer race having an opening defined in a peripheral wall of the outer race.
2. Description of Background Art
It is well known that some of needle roller bearings include an outer race formed with an opening for feeding a lubricant oil to internal component parts of the needle roller bearing and/or for mounting an engagement member for engagement with a shaft, such as disclosed in U.S. Pat. No. 3,316,037 and Japanese Examined Utility Model Publication No. 1-17707. By way of example, in a needle roller bearing designed for installation in a disc brake assembly, the outer race has such an opening for mounting the engagement member on/at the shaft through the needle roller bearing.
An example of prior art needle roller bearing is shown in FIG. 17. The illustrated prior art needle roller bearing includes an opening defined in the outer race and is generally utilized in association with a disc brake assembly. The outer race 1 is in the form of a shell of thin steel plate which has been deep drawn and includes a roller retainer 3 positioned inside the outer race 1 and carrying a plurality of needle rollers 2. The needle rollers 2 used therein are brought into rolling contact with an outer peripheral surface of a shaft 7 with no inner race employed between the roller retainer 3 and the shaft 7. As shown therein, the outer race 1 has the opening identified by 6 and defined therein in alignment with a through-hole 5 in the housing 4.
FIG. 18 illustrates a transverse sectional view of the prior art needle roller bearing shown in FIG. 17, the roller retainer 3 is in the form of a split ring having a split area 3a defined at a location aligned with the opening 6 in the outer race 1. An engagement member (not shown) engageable with the shaft 7 is inserted through the through-hole 5, then through the opening 6 and finally through the split area 3a.
The shell-like outer race 1 of the structure described above is press-fitted into the bore in the housing 4. However, since the outer race 1 is formed with the opening 6, and when the needle roller bearing is to be inserted under interference fit into the bore in the housing, for example, in a direction shown by the arrow Z in FIG. 17, a sharp edge 6af bar positioned on a peripheral lip region of the opening 6 in the outer race 1 at a location on a trailing side with respect to the direction Z of insertion of the outer race 1 tends to grind or scrape the inner peripheral surface of the bore in the housing 4 with resultant scrapes falling into the bearing. Once this occurs, a detrimental damage may occur in the system. Also, the edge 6af positioned on the peripheral lip region of the opening 6 at a location on a leading side with respect to the direction Z of insertion may often grind or scrape the inner peripheral surface of the housing 4 since one or more burrs are often formed on the edge 6af during the formation of the opening 6.
While the outer race 1 is made of steel plate, the housing 4 is generally made of aluminum for the purpose of reducing the weight of, for example, the disc brake assembly as a whole or made of iron which has not been heat-treated. Therefore, due to a difference in hardness between the outer race 1 and the housing 4, the above discussed problem associated with the grinding is very likely to occur. Also, while the opening 6 in the outer race 1 is generally formed by the use of a blanking technique, the presence of fins left at the peripheral lip region of the opening 6 highlights the above discussed problem of grinding.
Also, in the needle roller bearing wherein the roller retainer 3 has the split area 3a for the passage of the engagement member, it is necessary for the opening 6 in the outer race 1 to be aligned with the split area 3a with respect to the circumferential direction. However, since the roller retainer 3 is free to rotate inside the outer race 1, an accurate positioning of the split area 3a in the roller retainer 3 relative to the opening 6 in the outer race 1 is not easy to achieve during the assemblage and mounting of the needle roller bearing. Because of this, the adjustment in position of the roller retainer 3 relative to the outer race is generally carried out when the engagement member is inserted through the opening 6 in the outer race 1, and this positioning procedure is complicated and time-consuming because a space available for the adjustment to be done therein is extremely limited.
In addition to the foregoing problems, the use of the roller retainer 3 having the split area 3a brings about a problem in that, as compared with the roller retainer in the form of a hollow cylindrical member, the physical strength and the durability thereof tend to be reduced.
In an attempt to alleviate the foregoing problems, it has been suggested that, as shown by the double-dotted lines in FIGS. 17 and 18, the peripheral lip region 6b of the opening in the outer race 1 is bent to depress radially inwardly of the outer race 1. The use of the radially inwardly depressed peripheral lip region 6b does not only eliminate substantially the problem of grinding, but also the positioning procedure can be dispensed with since the depressed peripheral lip region 6b serves as a stop with which the split area 3a of the roller retainer is engaged. However, this suggestion still has a problem in that, since the roller retainer is in the form of the split ring having the split area as is the case with the roller retainer shown in FIGS. 17 and 18, the physical strength and the durability of the roller retainer are still remote from the requirement.